/* 清除浏览器默认边距，
使边框和内边距的值包含在元素的width和height内 */
 
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

/* 使用flex布局，让内容垂直和水平居中 */

section {
  /* 相对定位 */
  position: relative;
  overflow: hidden;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  /* linear-gradient() 函数用于创建一个表示两种或多种颜色线性渐变的图片 */
  background: linear-gradient(to bottom, #f1f4f9, #dff1ff);
}

/* 背景颜色 */

section .color {
  /* 绝对定位 */
  position: absolute;
  /* 使用filter(滤镜) 属性，给图像设置高斯模糊*/
  filter: blur(200px);
}

/* :nth-child(n) 选择器匹配父元素中的第 n 个子元素 */

section .color:nth-child(1) {
  top: -350px;
  width: 600px;
  height: 600px;
  background: #ff359b;
}

section .color:nth-child(2) {
  bottom: -150px;
  left: 100px;
  width: 500px;
  height: 500px;
  background: #fffd87;
}

section .color:nth-child(3) {
  bottom: 50px;
  right: 100px;
  width: 500px;
  height: 500px;
  background: #00d2ff;
}

.box {
  position: relative;
}

/* 背景圆样式 */

.box .circle {
  position: absolute;
  background: rgba(255, 255, 255, 0.1);
  /* backdrop-filter属性为一个元素后面区域添加模糊效果 */
  backdrop-filter: blur(5px);
  box-shadow: 0 25px 45px rgba(0, 0, 0, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.5);
  border-right: 1px solid rgba(255, 255, 255, 0.2);
  border-bottom: 1px solid rgba(255, 255, 255, 0.2);
  border-radius: 50%;
  /* 使用filter(滤镜) 属性，改变颜色。
  hue-rotate(deg)  给图像应用色相旋转 
  calc() 函数用于动态计算长度值 
  var() 函数调用自定义的CSS属性值x*/
  filter: hue-rotate(calc(var(--x) * 70deg));
  /* 调用动画animate，需要10s完成动画，
  linear表示动画从头到尾的速度是相同的，
  infinite指定动画应该循环播放无限次*/
  animation: animate 10s linear infinite;
  /* 动态计算动画延迟几秒播放 */
  animation-delay: calc(var(--x) * -1s);
}

/* 背景圆动画 */

@keyframes animate {
  0%, 100%, {
      transform: translateY(-50px);
  }
  50% {
      transform: translateY(50px);
  }
}

.box .circle:nth-child(1) {
  top: -50px;
  right: -60px;
  width: 100px;
  height: 100px;
}

.box .circle:nth-child(2) {
  top: 150px;
  left: -100px;
  width: 120px;
  height: 120px;
  z-index: 2;
}

.box .circle:nth-child(3) {
  bottom: 50px;
  right: -60px;
  width: 80px;
  height: 80px;
  z-index: 2;
}

.box .circle:nth-child(4) {
  bottom: -80px;
  left: 100px;
  width: 60px;
  height: 60px;
}

.box .circle:nth-child(5) {
  top: -80px;
  left: 140px;
  width: 60px;
  height: 60px;
}

/* 登录框样式 */

.container {
  position: relative;
  width: 400px;
  min-height: 400px;
  background: rgba(255, 255, 255, 0.1);
  display: flex;
  justify-content: center;
  align-items: center;
  backdrop-filter: blur(5px);
  box-shadow: 0 25px 45px rgba(0, 0, 0, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.5);
  border-right: 1px solid rgba(255, 255, 255, 0.2);
  border-bottom: 1px solid rgba(255, 255, 255, 0.2);
}

.form {
  position: relative;
  width: 100%;
  height: 100%;
  padding: 50px;
}

/* 登录标题样式 */

.form h2 {
  position: relative;
  color: #fff;
  font-size: 24px;
  font-weight: 600;
  letter-spacing: 5px;
  margin-bottom: 30px;
  cursor: pointer;
}

/* 登录标题的下划线样式 */

.form h2::before {
  content: "";
  position: absolute;
  left: 0;
  bottom: -10px;
  width: 0px;
  height: 3px;
  background: #fff;
  transition: 0.5s;
}

.form h2:hover:before {
  width: 53px;
}

.form .inputBox {
  width: 100%;
  margin-top: 20px;
}

/* 输入框样式 */

.form .inputBox input {
  width: 100%;
  padding: 10px 20px;
  background: rgba(255, 255, 255, 0.2);
  outline: none;
  border: none;
  border-radius: 30px;
  border: 1px solid rgba(255, 255, 255, 0.5);
  border-right: 1px solid rgba(255, 255, 255, 0.2);
  border-bottom: 1px solid rgba(255, 255, 255, 0.2);
  font-size: 16px;
  letter-spacing: 1px;
  color: #fff;
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.05);
}

.form .inputBox input::placeholder {
  color: #fff;
}

/* 登录按钮样式 */

.form .inputBox input[type="submit"] {
  background: #fff;
  color: #666;
  max-width: 100px;
  margin-bottom: 20px;
  font-weight: 600;
  cursor: pointer;
}

.forget {
  margin-top: 6px;
  color: #fff;
  letter-spacing: 1px;
}

.forget a {
  color: #fff;
  font-weight: 600;
  text-decoration: none;
}